1. Field of the Invention
The invention concerns a control cam or gear wheel comprising a plurality of layers of flat material stamped out or finely cut and placed one on top of the other in a sandwich-like manner. The invention also concerns a respective method for making such a cam or gear wheel.
2. Discussion of the Prior Art
A connecting rod comprising a plurality of layers of flat material stamped out or finely cut and placed one on top of the other in a sandwich-like manner for a reciprocating-piston internal combustion engine is disclosed, for example, in German reference DE 3841205 C2.
An external gear wheel comprising a plurality of layers of lamellar flat material placed flat one on top of the other is disclosed in German reference DE 3026685 A1, each individual layer of flat material having a plurality of openings, some of which are intended for receiving rivets to ensure in this way that the individual layers are held together.
A control cam comprising a plurality of layers of flat material connected to one another is known, for example, from German reference DE 4423107 A1.
The above-mentioned, known gear wheels or control cams consequently share the common feature that the individual layers of flat material are prepared by stamping or fine cutting. One disadvantage here may be the relatively high proportion of scrap, this disadvantage being all the more serious the greater the material thicknesses or grades of material used for the layers of flat material.
The invention is based on the object of providing a control cam of the generic type or a gear wheel of the generic type which makes it possible to use a reduced amount of material in comparison with conventional control cams and gear wheels. Furthermore, a method for respectively making them is to be provided.
According to the invention, it is provided that the individual layers of flat material altogether forming the control cam or gear wheel are of a multi-part form, with partition lines extending in the direction of the planes of layers of material. At least some of these partition lines of neighboring layers of flat material are arranged offset in relation to one another. Consequently, each individual layer of flat material is advantageously divided into at least 2 segments, which makes possible a material-saving arrangement of individual segments on a strip of material fed to a stamping die. To continue to ensure the strength of the control cam or gear wheel divided up into a greater number of individual parts by the segmentation of the individual layers of flat material, the individual segments are subsequently placed together to form the layers of flat material, the partition lines of one layer of flat material that extend between the individual segments being arranged offset in relation to the partition line or lines of other layers of flat material, preferably the neighboring layers.
It is preferably provided that the gear wheel is of a circular or annular form with a central opening, it in turn being preferred for the partition lines to be arranged extending radially from inside to outside.
It is also preferably provided that the individual segments are portions of a circular ring and at the same time bear a toothing on the outside and/or inside, so that, in the state in which they are placed together and one on top of the other, the gear wheel is produced. This may be both an externally toothed gear wheel and an internally toothed gear wheel or an annular gear bearing an external toothing and an internal toothing.
Such a construction according to the invention has, for example, considerable advantages in the preparation of internal gear pumps. While, until now, the outer ring, bearing the internal toothing, had to be adapted to the respective loading situation by making it from a high-grade metallic material by broaching, involving a correspondingly high loss of material, from now on this gear wheel is prepared from a plurality of layers of flat material which for their part in turn comprise segments. The segments can be stamped out in a closely interlinked manner and subsequently put together. The same applies to the inner wheel, provided with an external toothing.
Particularly preferably, each layer of flat material may comprise more than two, in particular three or four, segments, the partition lines of neighboring layers of the material lying approximately equally spaced apart in relation to one another.
For certain applications, it may be advantageous for the individual layers of flat material to be securely connected to one another in the state in which they are placed one on top of the other. For external gear wheels, for example, the necessary strength is provided in this way. For other applications, for example a pump delivering lubricating oil, however, it may be possible to dispense with a connection between neighboring layers of flat material, since the individual segments within the layers of flat material stabilize themselves in the installed state. In this case, it may be advantageous for assembly purposes to connect the individual segments of the layers of flat material to one another initially by means of pins, these pins subsequently being removed again.
For a further, preferred application, individual layers of flat material in the placed-together state may be of a cam-shaped form, the layers of the material, in the state in which they are placed one on top of the other, altogether forming the control cam according to the invention for the charge-cycle valve control of a reciprocating-piston internal combustion engine.
In this case, it may be provided that the individual segments of one layer of flat material are not identically designed, as for instance in the case of the gear wheel described above.
A method according to the invention for making a gear wheel or control cam of this kind provides that firstly a plurality of segments are stamped out or finely cut and subsequently the gear wheel or control cam is formed by grouping together a certain number of segments to give a layer of flat material and subsequently arranging a plurality of such layers of flat material one on top of the other to form a structural unit. The partition lines between the segments within each layer of flat material are not arranged in line one above the other but are offset in relation to one another, at least between some neighboring layers of flat material.
Depending on the number of segments per layer of flat material and depending on the intended purpose of the gear wheel or control cam, in this method each layer of flat material can firstly be formed by correspondingly placing the segments together, whereupon subsequently the gear wheel or control cam is completed by placing a plurality of such layers of flat material one on top of the other. However, as a departure from this, it may be advantageous firstly to stack a plurality of segments of neighboring layers of material one on top of the other and subsequently to complete the individual layers of flat material by adding further segments.
For production engineering reasons, it may also be advantageous already to provide during the stamping or fine cutting at least one receiving means in each segment for a connecting means. It is consequently possible during the grouping together for the individual segments to be threaded on, for example onto rod-shaped connecting means in the form of centering pins or spigots. These rod-shaped connecting means may additionally receive a rivet, which subsequently holds the flat material together, or may themselves be designed as a rivet, so that the connecting means is initially used for grouping together and subsequently remains permanently in the gear wheel or control cam for holding it together.